Search

The correlation between the event mean-transverse momentum [pT], and the anisotropic flow magnitude vn, ρ(vn2,[pT]), has been argued to be sensitive to the initial conditions in heavy-ion collisions. We use simulated events generated with the AMPT and EPOS models for Au+Au at sNN = 200 GeV, to investigate the model dependence and the response and sensitivity of the ρ(v22,[pT]) correlator to collision-system size and shape, and the viscosity of the matter produced in the collisions. We find good qualitative agreement between the correlators for the string melting version of the AMPT model and the EPOS model. The model investigations for shape-engineered events as well as events with different viscosity (η/s), indicate that ρ(v22,[pT]) is sensitive to the initial-state geometry of the collision system but is insensitive to sizable changes in η/s for the medium produced in the collisions. These findings suggest that precise differential measurements of ρ(v22,[pT]) as a function of system size, shape, and beam-energy could provide more stringent constraints to discern between initial-state models and hence, more reliable extractions of η/s.

The extended RΨm(2)(ΔS2) correlator is presented and examined for its efficacy to detect and characterize the quadrupole charge separation (ΔS2) associated with the purported Chiral Magnetic Wave (CMW) produced in heavy-ion collisions. Sensitivity tests involving varying degrees of charge separation injected into events simulated with the Multi-Phase Transport Model (AMPT) show that the RΨm(2)(ΔS2) correlators provide discernible responses for the background- and signal-driven quadrupole charge separation. This distinction could help identify CMW-induced quadrupole charge separation via measurements of the RΨ2(2)(ΔS2) and RΨ3(2)(ΔS2) correlators, relative to the second- (Ψ2) and third-order (Ψ3) event planes. The tests also indicate a sensitivity level that would allow for robust experimental characterization of possible CMW-induced charge separation.

A Multi-Phase Transport (AMPT) model is used to study the detection sensitivity of two of the primary correlators – Δγ and RΨ2 – employed to characterize charge separation induced by the Chiral Magnetic Effect (CME). The study, performed relative to several event planes for different input “CME signals”, indicates a detection threshold for the fraction fCME=ΔγCME/Δγ, which renders the Δγ-correlator insensitive to values of the Fourier dipole coefficient a1≲2.5%, that is larger than the purported signal (signal difference) for ion-ion(isobaric) collisions. By contrast, the RΨ2 correlator indicates concave-shaped distributions with inverse widths (σRΨ2−1) that are linearly proportional to a1, and independent of the character of the event plane used for their extraction. The sensitivity of the RΨ2 correlator to minimal CME-driven charge separation in the presence of realistic backgrounds, could aid better characterization of the CME in heavy-ion collisions.